Such cells are used, in particular, for analyzing the physical characteristics of pressure, volume and temperature of fluids from oil exploration wells, since a knowledge of these characteristics is fundamental in developing an oil field. Such cells are also used for analyzing light oils, for determining reservoirs, and also for various other applications such as investigating phase equilibrium, etc. They can be used for plotting various pressure curves as a function of temperature for given percentages of vapor phase relative to the total volume of fluid.
One such cell, described in U.S. Pat. No. 2,380,082 comprises a strong vertical cylindrical envelope having two superposed chambers therein, which chambers are in communication with each other, and the lower chamber has the smaller diameter. The envelope is provided with portholes looking into the lower chamber and with graduations for showing and measuring the level of the separation surface between the liquid phase and the gas phase of the fluid under investigation. The upper chamber includes a freely-mounted piston which divides said upper chamber into two portions. The upper portion is filled with mercury via a mercury pump and enables desired measuring pressures to be exerted on the free piston. The bottom end of the bottom chamber is also fed with mercury in order to bring the gas-liquid separation surface in the fluid under investigation to a suitable level. The liquid phase of said fluid is in direct contact with the mercury which acts as a piston. The cell is placed in a heated enclosure.
Such apparatus has the drawback of using mercury which is a dangerous material and which requires heavy equipment, in particular for pumping purposes. Further, the direct interface in the bottom chamber between the mercury and the liquid phase of the fluid under investigation requires special precautions to be taken or special equipment when the cell is being emptied of the fluid under investigation in order to ensure that only said fluid is removed without any mercury being mixed in. Finally, some fluids may contain components which react or form alloys or amalgams with mercury.
The present investigation thus seeks to provide such a cell which does not require the use of any mercury.